This invention relates to an injector for use in supplying fuel to a combustion space of an internal combustion engine. The invention relates, in particular, to an injector of the outwardly opening type suitable for use in supplying fuel to an engine of the compression ignition type.
Part of a typical injector of the outwardly opening type is illustrated in FIG. 1. As shown in FIG. 1, the injector comprises a needle 1 slidable within a bore 2 formed in a nozzle body 3. The bore 2 defines a seating with which the needle 1 is engageable to control the supply of fuel to a chamber 4. The position of the needle 1 also determines how many of a plurality of outlet openings 5 communicate with the chamber 4.
Part of the needle 1 downstream of the seating is of diameter substantially equal to the adjacent part of the bore 2 and engagement therebetween guides movement of the needle 1. It has been found, however, that fuel may leak between this part of the needle 1 and the bore resulting in inefficient combustion of fuel and high levels of emissions. Where the injector is used with a fuel system of the direct injection type, the level of leakage may be increased due to dilation of the bore 2.